The present invention relates generally to a method and system for detecting thermal asperities on discs used in disc drives. More particularly, the present invention relates to a method and system for detecting thermal asperities that utilizes adaptive threshold levels that vary from transducer to transducer and from position to position along a disc.
In disc drive data storage devices, digital data is written to and read from a thin layer of magnetizable material on a surface of one or more rotating discs. Write and read operations are performed through a transducer which is carried on a slider body. The slider and transducer are sometimes collectively referred to as a head, and typically a single head is associated with each disc surface. When the transducer is a magnetoresistive (MR) type sensor, the combination of the slider and the transducer are frequently referred to as an MR head. The heads are selectively moved under the control of electronic circuitry to any one of a plurality of circular, concentric data tracks on the disc surface by an actuator device. Each slider body includes an air bearing surface and, as the disc rotates, the disc drags air beneath the air bearing surface which develops a lifting force that causes the head to lift and fly several microinches above the disc surface.
In operation, the head can come into contact with asperities on the surface of the disc while the head flies above the surface of the disc. Potentially, this undesirable contact can cause data written to a particular location on the disc to be lost. Immediately after contact with an asperity, the heat generated by the contact changes the resistive properties of the MR sensor. As a result, the corresponding signal read by the MR head is distorted by a voltage spike and subsequent decay, sometimes causing the data stored near the asperity to be unrecoverable. The voltage spike in the read signal is frequently referred to as xe2x80x9cthermal asperity,xe2x80x9d while the defect on the disc is referred to as an xe2x80x9casperityxe2x80x9d. However, since one is indicative of the other, the two terms are frequently used interchangeably.
Disc asperities which are located in the factory during a defect scanning process can be recorded in a disc drive""s primary defect list so that the drive does not store data at those locations. Currently the defect scanning process is carried out using a thermal asperity sensor mounted on an air bearing surface of a slider. The air bearing surface is positioned a small distance from the surface of a rotating disc to be tested. The thermal asperity sensor can move along the radius of the disc to detect thermal asperities from the outer diameter to the inner diameter of the disc. The thermal asperity sensor is operatively coupled to a testing apparatus. The testing apparatus has a preamplifier with a thermal asperity detection function. A threshold level is set in the preamplifier. The threshold level is fixed for all heads in all drives. If a reading from the sensor is greater than the fixed threshold level, it is saved as a detected thermal asperity.
The prior art method of using a fixed threshold level has several disadvantages. Primarily head amplitudes vary not only from head to head but also in each head as it is moved from an outer diameter of a disc to the disc""s inner diameter. Also, the level of the amplitude detected by the preamplifier is affected by the preamp""s gain and process variation. In addition, the slope and range of the programmable thermal asperity threshold varies from one vendor""s preamplifier to another vendor""s preamplifier.
Furthermore, if the threshold level is not properly set, false detections may occur. For example, noise may be improperly classified as a thermal asperity and logged as a defect. As a result, data will not be written to that portion of the disc. This has the disadvantage that usable areas of a disc are not used. This is particularly disadvantageous if the number of false detects is large.
Accordingly, there is a continual need for improvements in the art whereby the detection of thermal asperities can be optimized and false detects can be reduced. In addition, there is a need for a method and system of thermal asperity detection that takes into account variations in vendor parts, variations in transducers as well as disc location variations.
The present invention provides a solution to the above and other problems and offers the above and other advantages over the prior art.
The present invention relates to a method and system which solves the above-mentioned problems and offers the above mentioned advantages. More particularly, the present invention relates to method of adaptively setting a threshold level for a disc drive system to test for thermal asperities. In one embodiment, the method includes the steps of determining a first threshold level for a first transducer in a first track and determining a second threshold level for the first head in a second track. In another embodiment, the method includes the steps of determining a first threshold level for a first head in a first track and determining a second threshold level for a second head in the first track.
In still another embodiment, the method includes the steps of determining a threshold level for a first head in a first track, determining a threshold level for the first head in a second track and saving the threshold levels for the first head. The steps of determining the threshold level for the first head include initially setting the threshold level at a minimum threshold level, determining whether a detection is made at that threshold level. If a detection is made at that level, increasing the threshold level by an increment and determining whether a detection is made at the incremented threshold level. These steps are repeated until a threshold level is reached where a detection is not made in order to not detect noise.
In another embodiment of the invention, there is provided a system for adaptively setting a threshold level for a disc drive to test for thermal asperities. The system includes a programmable controller that is programmed to determine a threshold level for a first transducer in a first track and a second track. The threshold level is initially set at a minimum threshold level and is subsequently increased until a detection is not made. The threshold levels for the first transducer are saved in a memory.
Accordingly, the present invention provides a method and system of detecting thermal asperities while reducing the likelihood of false detects thereby improving the amount of the disc that is usable.
Another advantage of the present invention is that it provides a more accurate asperity defect mapping. In addition, it eliminates the inflexibility of using a fixed threshold for all heads at all positions along disc.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.